Chapter 4- Alternative Photosynthetic pathways

Question 1

C3 Photosynthesis

Answer 1

-normal photosynthesis, 3-carbon PGA is produced

Question 2

C4 Photosynthesis

Answer 2

• produces 4-carbon oxaloacetate; occurs in HOT environments
• Carbon dioxide is spatially isolated to prevent photorespiration

Steps:

1. PEP carboxylase fixes CO2 into a 3-carbon PEP molecule, producing oxaloacetate (C4), then converted into malate in mesophyll cells
2. Malate is transferred to bundle sheath cells, which have lower concentrations of oxygen.
3. Malate is decarboxylated to release CO2, spatially isolating where CO2 is fixed by RuBisCo. Drawback: pyruvate is also produced shuttled back into mesophyll cells.
4. Pyruvate is converted back into PEP by using ATP energy.

Question 3

CAM (Crassulacean Acid Metabolism) photosynthesis

Answer 3

-temporal isolation of CO2 to prevent photorespiration in HOT environment

1. During the day, stomata are always closed to prevent transpiration (exit of water)
2. During the night, stomata opens to let CO2 in. PEP carboxylase fixes the CO2 into PEP, producing oxaloacetate and then into malate. Malate is stored in vacuoles.
3. During the next day, they close stomata and Malate is converted oxaloacetate releasing CO2 and PEP. CO2 is dropped off at RuBP to begin Calvin Cycle

Question 4

Anoxygenic Photosynthesis

Answer 4

-used by non-plants and does not use water as initial electron source!
Ex: Green and Purple sulfur bacteria